Bistable optical device

ABSTRACT

A bistable optical display device comprising a reflective anode, such as silver, and a metal cathode, such as zinc, immersed in a caustic electrolyte, such as potassium hydroxide. Application of a &#39;&#39;&#39;&#39;turn-on&#39;&#39;&#39;&#39; voltage of approximately 1.5 volts causes a chemical reaction such that the reflective anode turns substantially non-reflective. This condition persists even if the &#39;&#39;&#39;&#39;turn-on&#39;&#39;&#39;&#39; voltage is removed and the cell will return to its original state only if the anode and cathode are shorted together.

United States Patent 1 1 Sharp 1H1 3,745,538 [451 July 10, 1973 BISTABLE OPTICAL DEVICE [75] Inventor: Donald Jex Sharp, Lawrence Township, Mercer County, NJ.

[73] Assignee: Western Electric Company,

Incorporated, New York, N.Y.

[22] Filed: June 1, 1971 [21] Appl. No.: 148,516

[52] US. Cl. 340/173 CH, 340/173 LM [51] Int. Cl Gllc 13/02 [58] Field of Search 340/173 CH [56] References Cited UNITED STATES PATENTS 3,060,317 10/ 1962 Winogradoff 340/173 CH 3,363,239 1/1968 Alexander 340/173 Primary ExaminerTerrell W. Fears AttorneyW. M. Kain, J. B. l-loofnagle, Jr. and R. C. Winter [57] ABSTRACT A bistable optical display device comprising a reflective anode, such as silver, and a metal cathode, such as zinc, immersed in a caustic electrolyte, such as potassium hydroxide. Application of a tum-on" voltage of approximately 1.5 volts causes a chemical reaction such that the reflective anode turns substantially nonreflective. This condition persists even if the turn-on voltage is removed and the cell will return to its original state only if the anode and cathode are shorted together.

9 Claims, 4 Drawing Figures BISTABLE OPTICAL DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention Broadly speaking, this invention relates to a bistable device. More particularly, in a preferred embodiment, this invention relates to a bistable optical display and storage device which utilizes a metal electrode of controlled reflectivity to generate the readout.

2. Discussion of the Prior Art In computer systems, and the like, it is frequently desired to present an optical readout of selected analog or digital information stored within the system. Various techniques and apparatus have heretofore been utilized for this purpose, including glow-discharge devices, liquid crystals, tungsten filament lamps, cathode ray tubes, and various solid-state light emitting diodes, and the like. Unfortunately, all of the above devices suffer from one or more disadvantages, such as low levels of light output, high cost, and a continuous current drain when in an activated state. With the advent of the minicomputer, and more recently the pocket computer, the problem of providing a readout device which is simple in design and inexpensive to produce, yet which provides a highly visible readout with a negligible current drain when in the activated state, has become particularly acute. Fortunately, this problem has been solved by the instant invention which, in one embodiment, comprises a bistable optical device having a metallic anode and a metallic cathode immersed in an electrolyte. The metallic anode has at least one normally reflective surface while the metallic cathode is comprised of a metal dissimilar to the anode. Upon establishment of a d.c. potential between the anode and the cathode, the normally reflective surface of the anode becomes substantially non-reflective. When the anode and the cathode are shorted together, the anode again becomes reflective.

The invention and its mode of operation will become more fully understood from the following detailed description and the drawings in which:

FIG. 1 is a partially schematic, partially crosssectional view of one embodiment of the invention;

FIG. 2 is a diagram of the electrical waveforms which may be found in the embodiment shown in FIG. 1;

FIG. 3 is an isometric, partial view of another embodiment of the invention; and

FIG. 4 is a partially schematic, partially diagrammatic view of yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, an illustrative embodiment of the invention comprises an optical readout and storage device having a metallic anode ll, comprised, for example, of silver, and a metallic cathode l2, comprised, for example, of zinc, immersed in a caustic electrolyte 13, for example, a potassium or sodium hydroxide solution which has been saturated with zinc oxide. At least one surface of anode 11 is polished to form a mirrored surface, and anode ll, cathode l2 and electrolyte '13 are contained within a sealed enclosure 16, for example, an enclosure fabricated from an opaque glass, or plastic. One wall of the enclosure is provided with a transparent window portion 17, for example, of glass or plastic, and anode 11 is so positioned within the enclosure that the polished surface thereof is visible through the window. Anode 11 and cathode 12 are connected to a pair of conductors l8 and 19, respectively, which pass through the walls of enclosure 16 in such a manner that the electrolyte cannot leak from the enclosure.

Conductor 18 is connected, via a pair of normally open contacts 21 of a double-pole, double-throw switch 22, to the positive terminal of a d.c. source 23, for example, a battery. The negative terminal of d.c. source 23 is connected directly to conductor 19, and hence, to the cathode of device 10. Conductor 18 is also connected, via a pair of normally closed contacts 24 on switch 22, to the negative terminal of d.c. source 23.

- In operation, light from any suitable source, for example, from an incandescent bulb 26 and a lens 27, is directed through window 17 onto the polished surface of anode 11, where it is reflected off and back out through window 17 to any suitable light-sensitive device, or to the eye 20 of a human observer. It will be appreciated that the light source shown is merely illustrative and that many other light sources may be employed, for example, sunlight, or the light from a laser beam, a fluorescent bulb, or an arc lamp. Similarly, any conventional light-sensitive device may be substituted for eye 20, for example, a photo-electric cell or any of the several photo-sensitive solid-state devices currently available. It will also be appreciated that the degree to which anode 11 is .polished depends, to a certain extent, on the intensity of the incident illumination. If the latter is strong enough, even a fairly rough, unpolished surface will reflect sufficient light to make the device operative.

With switch 22 positioned to the right, as shown, both anode l1 and cathode 12 of device 10 will be at the same potential (via switch contacts 24) and the polished surface of anode 11 will act as a mirror, reflecting substantially all of the light which is incident thereon from lamp 26. There will, of course, be the customary, minor, light transmission losses experienced in twice passing through window 17, as well as the customary 5 to 10 percent loss at the mirrored surface of anode 11. Thus, the observer will clearly see illumination from, or an image of, light source 26 reflected off the mirrored surface of anode 11. However, with switch 22 thrown to the left, anode 11 will no longer be connected to cathode 12 thereof, but rather, to the positive terminal of d.c. source 23. There will, thus, be a potential difference established between anode l1 and cathode 12. This potential difference will cause a chemical reaction within device 10 and the formation of a black silver oxide (Ag O) on the mirrored surface of anode 11. As a result of the formation of this black oxide, anode 11 will cease to act as a mirrored surface, and light transmission through device 10 will drop from its previous value of about percent of the incident light to a value of about 20 percent, or less. The overall reaction for a device comprised of the illustrative metals and electrolyte given, is of the form:

Ago -I H2O 2c :2 2Ag 20H- (Black) (Reflective) For a silver anode, a zinc cathode, and a caustic, potassium hydroxide electrolyte, the potential of source 23 should advantageously lie within the range of about 1.5 to 1.9 volts. Below about 1.5 volts,.the reaction in the cell is unreliable, and above about 1.9 volts, undesirable heating effects, and the production of unwanted gases may occur. The exact turn on-turn off voltage is, of course, a function of the particular metals employed for the cathode and anode. For example, with a cadmium cathode, the voltage range will be from approximately 1.2 to 1.5 volts. Another material that can be used for the cathode is iron.

Importantly, device exhibits a highly desirable memory characteristic in that, even if the potential of source 23 is removed, device 10, nevertheless, continues to exhibit a potential across its electrodes of approximately volts, for long periods of time, provided that no substantial current drain is imposed upon the cell. However, if switch 22 is thrown again to the right, thereby shorting anode 11 to cathode 12, the reaction will reverse itself and the surface of anode 11 will again become reflective, returning device 10 to its original or starting position.

FIG. 2 depicts the voltage waveforms which may be expected with the circuit shown in FIG. 1. Waveform 28 represents the turn-on potential of 1.6 volts applied for approximately 200 ms. Waveform 29, in turn, represents the potential developed by the cell after the turn-on potential has been removed. The exact "turn-on" and turn-off time is related to the anode area and the cells internal resistance. For example, cells comprising reduced anode areas would be expected to exhibit a proportional reduction in transition time. It will be noted that in FIG. 2 waveform 29 slopes gradually down to the right. This fall off has been greatly exaggerated in the drawing. Actually, the device is stable for at least a week and more typically holds relatively constant at 1.55 volts for many weeks, then drops suddenly to zero. In this regard, the device behaves not unlike a battery with a long shelf life.

In the example shown in FIG. 1, switch 22 is depicted as a mechanical switch. However, switch 22 is merely intended to be representative of the various solid-state logic and switching circuits which could be employed to gate device 10 on and off. It is an important aspect of the invention that, because the potential required to change the state of device 10 is only in the order of 2 volts, or less, device 10 can be integrated, for example, with conventional transistorized circuitry, to produce a compact readout package.

FIG. 3 illustrates another embodiment of the invention, particularly well suited for displaying symbols, such as numeric or alphabetic characters. As shown, numeric readout device 10' includes a cathode 12 and an anode 13' comprising an insulating substrate 31, upon which a plurality of metallic elements 32 are arranged, in a conventional manner. Each element 32 is connected, by a lead 18, to an individual logic circuit (not shown) similar in operation to switch 22 in FIG. 1. By the generation of appropriate control signals, from conventional control circuitry (not shown), selected ones of elements 32 may be connected to .a dc. source to display the desired numeric character, for example, the numeral 3, through window 33, as shown in FIG. 3. Substrate 31 may comprise a solid substrate, such as ceramic, or a porous substrate to increase the area of the elements 32 in contact with the electrolyte, thereby providing greater total charge retention where this is required.

FIG. 4 illustrates yet another embodiment of the in- 6 vention, in which light from an optical maser, or laser 41, is passed through filter 42 (optional), to reduce its intensity, and then focused by a lens 43 onto the mirrored surface of anode 11. Lead 18, from anode 11, is connected to the output of a first gating circuit 44 having a 0" input 45, and to the output of a second gating circuit 51 having a 1" input 46. A power supply 48 has a negative terminal which is grounded, and a positive terminal which is connected, via a lead 49, to the power input terminal of gating circuit 44. Lead 49 also connects power supply 48 to gating circuit 51, and to the power input of a buffer amplifier 60 whose input is also connected, via lead 18, to anode 11 of device 10. A lead 63 connects 0 lead 45 to the reset input of gating circuit 51. A timing circuit 47 is associated with gating circuit 44. As previously discussed, the light beam from laser 41 is reflected off the mirrored surface of anode 11 and focused by an optional lens 53 onto a screen 54, or other suitable display device.

The operation of the embodiment illustrated in FIG. 4 is essentially similar to that discussed with respect to FIG. 1. The application of a 1" signal to gating circuit 51 via lead 46 causes that circuit to close an internal current path between lead 18 and ground, thereby placing anode 11 and cathode 12 of device. 10 at the same potential. Thus, the mirrored surface of anode 11 will reflect substantially all of the light from laser 41 onto display screen 54. However, application of a 0 signal to lead 45 is fed, via lead 63, to gating circuit 51 to break the connection between lead 18 and ground, and at the same time, causes gating circuit 44 to close an internal connection between the positive potential on lead 49 and conductor 18, thereby establishing a potential difference between the electrodes of the device 10, causing the mirrored surface of anode 11 to be come blackened, and hence, non-reflective, as discussed in connection with FIG. 1. After 200ms, for example, timing circuit 47 resets gating circuit 44, so that the internal connection between leads 49 and 18 is broken. However, if the signal on 0 lead 45 is itself a pulse signal, timing circuit 47 may be omitted. Gating circuits 44 and 51 and timing circuit 47 may be any conventional circuit capable of providing the function desired, for example, a flip-flop, AND-gate, etc., etc. After the potential has been removed from anode 11, buffer amplifier 60 will sense the potential developed by cell 10, and the previously mentioned memory feature may be obtained by interrogating the output lead 61 of amplifier 60.

One skilled in the art will appreciate that the invention disclosed has many practical applications, for example, it may be used in the entertainment industry to produce a television display, or in the communications industry as an optical modulating device, or as a radar readout device, etc. One skilled in the art may also make varous changes and modifications to the illustrative embodiment shown, without departing from the spirit and scope of the invention.

We claim:

1. An optical device, which comprises:

an electrolyte selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide; a silver anode, having a normally reflective surface,

immersed in the electrolyte; and Q a cathode, comprising a metal selected from the group consisting of zinc, cadmium and iron, immersed in the electrolyte, the surface of the anode becoming oxidized and substantially non-reflective when the anode is connected to an external potential source that is positive with respect to the cathode, the oxide being reduced and the surface of the anode again becoming reflective when the anode is connected to the cathode externally of the device.

2. An optical device, which comprises:

a housing having a transparent window;

a transparent electrolyte, contained in the housing, selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide;

a silver anode immersed in the electrolyte, the anode having a normally reflected surface that is visible through the window;

a cathode immersed in the electrolyte, the cathode comprising a metal selected from the group consisting of zinc, cadmium and iron;

circuitry for connecting the anode to an external potential source that is positive with respect to the cathode so that the anode surface is oxidized to become substantially non-reflective; and

circuitry for connecting the anode to the cathode so that the oxide is reduced and the surface of the anode again becomes reflective. v

3. An optical readout and storage system which comprises:

an optical device including a normally reflective silver anode, a cathode comprising a metal selected from the group consisting of zinc, cadmium and iron, both anode and cathode being immersed in an electrolyte selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide;

means for directing a beam of light onto the anode, the beam being reflected away from the device by the anode;

means for applying'a momentary potential between the anode and the cathode to cause the anode to oxidize and change from reflective to substantially non-reflective, whereby the reflected beam is sub- 6 stantially extinguished; and

means for connecting the anode to the cathode to reduce the oxide on the anode and cause the anode to change from substantially non-reflective to reflective.

4. A symbol display device, which comprises:

an electrolyte selected from the group comprising a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide;

a plurality of silver anodes immersed in the electrolyte, each anode having a reflective surface, the anodes being positioned to array the reflective surfaces in a predetermined spatial pattern; and

a cathode, comprising a metal selected from the group consisting of zinc, cadmium and iron, immersed in the electrolyte, a momentary potential applied between a particular one of the anodes and the cathode causing the particular anode surface to oxidize and become substantially non-reflective, whereby a symbol can be displayed by applying the momentary potential to selected anodes.

5. The optical device according to claim 2 wherein the cathode comprises zinc and the external potential source is within the range of 1.4 to 1.9 volts d.c.

6. The optical device according to claim 2 wherein the cathode comprises cadmium and the external potential source is within the range of 1.2 to 1.5 volts d.c.

7. The system according to claim 3 further comprismg:

means, connected. to the cathode and the anode, for detecting the presence or absence of a potential thereacross, whereby the status of the optical device can be determined.

8. The system according to claim 3 wherein the cathode is zinc; the momentary potential is within the range of 1.4 to 1.9 volts d.c. and is applied for not more than 200 milliseconds.

9. The system according to claim 3 wherein the cathode is cadmium; the momentary potential is within the range of 1.2 to 1.5 volts d.c. and is applied for not more than 200 milliseconds. 

1. An optical device, which comprises: an electrolyte selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide; a silver anode, having a normally reflective surface, immersed in the electrolyte; and a cathode, comprising a metal selected from the group consisting of zinc, cadmium and iron, immersed in the electrolyte, the surface of the anode becoming oxidized and substantially nonreflective when the anode is connected to an external potential source that is positive with respect to the cathode, the oxide being reduced and the surface of the anode again becoming reflective when the anode is connected to the cathode externally of the device.
 2. An optical device, which comprises: a housing having a transparent window; a transparent electrolyte, contained in the housing, selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide; a silver anode immersed in the electrolyte, the anode having a normally reflected surface that is visible through the window; a cathode immersed in the electrolyte, the cathode comprising a metal selected from the group consisting of zinc, cadmium and iron; circuitry for connecting the anode to an external potential source that is positive with respect to the cathode so that the anode surface is oxidized to become substantially non-reflective; and circuitry for connecting the anode to thE cathode so that the oxide is reduced and the surface of the anode again becomes reflective.
 3. An optical readout and storage system which comprises: an optical device including a normally reflective silver anode, a cathode comprising a metal selected from the group consisting of zinc, cadmium and iron, both anode and cathode being immersed in an electrolyte selected from the group consisting of a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide; means for directing a beam of light onto the anode, the beam being reflected away from the device by the anode; means for applying a momentary potential between the anode and the cathode to cause the anode to oxidize and change from reflective to substantially non-reflective, whereby the reflected beam is substantially extinguished; and means for connecting the anode to the cathode to reduce the oxide on the anode and cause the anode to change from substantially non-reflective to reflective.
 4. A symbol display device, which comprises: an electrolyte selected from the group comprising a solution of potassium hydroxide saturated with zinc oxide and a solution of sodium hydroxide saturated with zinc oxide; a plurality of silver anodes immersed in the electrolyte, each anode having a reflective surface, the anodes being positioned to array the reflective surfaces in a predetermined spatial pattern; and a cathode, comprising a metal selected from the group consisting of zinc, cadmium and iron, immersed in the electrolyte, a momentary potential applied between a particular one of the anodes and the cathode causing the particular anode surface to oxidize and become substantially non-reflective, whereby a symbol can be displayed by applying the momentary potential to selected anodes.
 5. The optical device according to claim 2 wherein the cathode comprises zinc and the external potential source is within the range of 1.4 to 1.9 volts d.c.
 6. The optical device according to claim 2 wherein the cathode comprises cadmium and the external potential source is within the range of 1.2 to 1.5 volts d.c.
 7. The system according to claim 3 further comprising: means, connected to the cathode and the anode, for detecting the presence or absence of a potential thereacross, whereby the status of the optical device can be determined.
 8. The system according to claim 3 wherein the cathode is zinc; the momentary potential is within the range of 1.4 to 1.9 volts d.c. and is applied for not more than 200 milliseconds.
 9. The system according to claim 3 wherein the cathode is cadmium; the momentary potential is within the range of 1.2 to 1.5 volts d.c. and is applied for not more than 200 milliseconds. 